Method and apparatus for use in the digestion of fibrous material



Oct. 16, 1934. T. B R 1,977,379

METHOD AND APPARATUS FOR USE IN THE DIGESTION OF FIBROUS MATERIAL Filed July 12. 19 32 2 Sheets-Sheet 1 INVENTO/T ATTORNEY Oct. 16,1934. LDUNBAR 1,977,379

METHOD AND APPARATUS FOR USE IN THE" DIGEST-ION OF FIBROUS MATERIAL Filed July 12, 1932 2 sheets-sheet 2 JAM; Q ill ATTOR Y Patented Oct. 16, 1934 PATENT OFFICE METHOD AND APPARATUS FOR USE IN THE DIGESTION OF FIBROUS MATERIAL Thomas L. Dunbar, Watertown, N. Y.

Application July 12, 1932, Serial No. 622,083

: 20 Claims.

The present invention relates to the production of wood pulp for use in the manufacture of paper, and more particularly to an improved method and apparatus for circulating and heating digester liquors during thedig'estion' or cookmg process.

An object of my invention is the provision of an improved method and apparatus for the digestion of fibrous material, and particularly for circulating and heating the digester liquor. I provide means for utilizing spent liqu'ors from previous cooks for a preliminary hearing of the digester liquor, utilizing the same lines and pump in draining the digester liquor and in supplying heat to the heating means. I further provide a novel method and apparatus for heating digester liquor.

An embodiment of my invention is illustrated in the accompanying drawings, in which: 20 Fig. 1 is a diagrammatic elevational view of a preferred form of apparatus, certain parts being omitted for the sake of clearness;

Fig. 2 is an elevational view, partly broken away, of my heat exchanger;

Fig. 3 is a perspectiveview, partly broken away, showing in detail a-section of the heater; and

Fig. 4 is a plan view of the end plate of the heater.

Referringto the drawings and especially to Fig. 1, the numeral 1 indicates a pulp digester. .While a system comprising three digesters is illustrated in the drawings, any. number of digesters may be similarly connected. Each digester is provided with a'top relief line 31 leading through the relief header 36. Each digester is further provided with a side relief line 33 having therein the'bottom of the accumulator 3. The eductor 3'7 is supplied with raw or partially prepared cooking' acid by means 39 and 40.

The suction end of the circulating line 15, provided with the valve 6, communicates .with the interior of the digester at a .point near the top of the digester. The end of the suction line, inside the digester, is provided with a strainer (not shown). The line 15' connects with the line 16 leading to the suction side. of the pump 5. This I pump discharges into the line 48, which line leads either through the v'alve 12 to the line 22 or through the valve 11 to the heat exchanger 4 which will be described in detail at a later point,

- taminated condensate passes through the line 26 valve 32 to the branch line 35 and thence to the of the 'pump 30 and the lines from the heater 4 iscarried by the line 25 to the selecting apparatus 24, from which any condensate that has been contaminated discharges through the line 27'to the sewer, while unconand the header 28 to the hot well.

The selecting apparatus 24 comprises a small tank containing electrodes which are connected on the outside with a valve mechanism, so that when the electrical resistance of the material within the chamber changes the connected valves are actuated. If there is any acid contained in the liquor the conductivity thereof becomes relatively higher and the valve in the line 2'7 is opened and the contaminated liquor is passed to the sewer, but if the liquor is uncontaminated, .80 the valve in the line 26 is opened and the liquor is passed through the line 28 to the hot well.

A vessel 2 is provided for storing the spent liquor extracted from the digesters atthe end of the cook, and this liquor is afterwards utilized in the heater 4 as a heating medium. The vessel 2 is connected by the header 22 and the branch 20 having therein the valve 10-, with the line 23 leading into the exchange heater 4. The line 25 is adapted to carry spent liquor from the heater to the selecting apparatus '24, in the same manner as it carries steam condensate. The header 22 also connects through the valve 13 withthe line 16.

The acid filling line 44 leads from the accumu- '95 lator 3 to the pump 29, which pump discharges through the line 43, branches 42 and valves 41 into the bottom of the digesters. The heat exchanger 4, asillustrated in Figs. 2, 3'and 4, is made up of a series of sections or plates 61, one of which is shown in detail in Fig. 3. Each section has a circular rim 62 and a central hub 78 which are joined by the rib '77. Halves of the casting are offset as indicatedby theofifset line '76 in Fig. 3, so that in the plate, as shown in Fig. 3, the lip of the farther half of the casting is above the lip of the nearer half. The rim 62 is provided with extended perforated ears 66. The hub is perforated at '75.

Integral with the rim and the hub, each section has a pair of oppositely-disposed semicircular metal sheets 63 and 64 presenting helically sloping surfaces. The surface of the sheet the ears 66 and through the central perforations '75, andattaching nuts '71 on the ends thereof.

[n this assembled position the edges of the sheets 63 and 64 overlap as shownin Fig. 2, that is, the edge of the sheet 63 of one section overlaps the edge of the sheet 64 of the next lower section. The end plates 80 of the assembled heater, shown in Fig. 4, are fiat and present apertures 52, 53 in the top plate and 54, in the bottom plate. The line 23 is connected at 53 and the line 25 at 55. The line 11 is connected at 54 and the line 17 at 52.

The assembled heater, as illustrated in Fig. 2, presents a pair of passages contiguous throughout their lengths, helically sloping and mutually and alternately interposed. The heating medium enters throughthe connection at 53 and passes down through one of the passages and out through the connection at 55. The liquid to be heated enters through the connection at 54,

and passes up through the other passage and out through the connection at 52, as indicated by the arrows in Fig. 2. i

In heating circulating digester. liquors, it has heretofore been the practice to construct the heater passages through which the liquor is passed of circular cross section. This construction results in minimum heating surface for a given volume of liquor flowing through the heater passage. By constructing the passages of my heater of unequalcross-sectionaldiameter in different directions, I increase the effective heating area for a given volume of liquor and the heating of the liquor is thereby accomplished much more effectively. Various arrangements of the .passages are possible, but I prefer the helically-sloping arrangement shown.

It is highly desirable that heaters for digester liquors-particularly for acid liquors-be readily accessible for cleaning, that the heat be distributed to both sides of the chamber containing the liquor that is to be heated, and that the liquor pass through the exchange heater at a relatively high velocity so that the resulting scouring action will prevent the deposition of pitch and earth salts contained in the cooking liquor. My heater is so designed as to accomplish these ends. Under ordinary operation the heater is practically selfcleaning, but if cleaning is required itis merely necessary to remove'the bolts '70, when the sections maybe separately removed for cleaning.

When intended for use withsulphite liquors, the

heater is preferably made of acid-proof material I such as acid-proof steel, but when intended for use in connection with'alkaline liquors ordinary cast steel or cast iron may be used.

Operation in accordance with my invention may be as follows:

Any digester is. filled with chips in the normal manner and 'hot cooking liquor is supplied thereto from the accumulator 3. Or cold liquor may be supplied from a storage tank. The digester is then sealed in, the valves 6, 11 and '7 are opened and the valves 8, l2 and 13 are closed.' If stored spent liquor from a previous cook is available,

the valve 9 is closed and the valve 10 opened- 9.

allow this liquor to flow from the storage tank 2 through the exchange heater 4. At the same time the pump 5 is started and liquor is drawn from the top of the digester through the lines 15 and 16 to the pump 5 from which it is discharged through the line 48 and valve 11 to the exchange heater 4. The heated liquor is discharged through the lines 17 and 49, the valve 7 and the branches 14 into the bottom of the digester. The inlets to the digester at the ends of the branches 14 are relatively large, and the pump 5 is preferably a low head pump, so that the circulating liquor enters the digester at a low velocity. Due to the suction at the top and the continual pumping in at the bottom the liquor gradually rises through the pulp mass to the suction connection on the upper end of the line After the contents of the vessel 2 have been exhausted the valve 10 is closed and the valve 9 is opened, admitting steam from theline 21 to the exchange heater and the heating is continued with steam as a heating medium.

If an acid accumulator is used, the relief connections 31 and 33 are operated in accordance with the disclosure of the copending application of T. L. Dunbar and A. D. Merrill, Ser. No. 576,254, filed November 20, 1931, now Patent No. 1,918,459, dated July 18, 1933, and the operation of these connections is not part of the present invention. If no acid accumulator is used, the

. header 36 is connected to a cooler (not shown) and the cooled gases and liquors are discharged from the cooler to an acid storage tank.

Side relief liquor drawn off at the end of the cook should not be sent to the accumulator 3. The valve 13 enables the operator to bypass the pump 5 and lead the side relief directly to the hot liquor storage tank 2, at this or any other stageof the operation.

After the contents of, the digester have been cooked to the proper point, the valves 6, 9 and 11 are closed and the valves '7, 8 and 12 are opened. The pump 5 is kept running, withthe result that the spent liquor is extracted from the digester through the branches 14, line 49, valves '1 and 8 and line 16 to the suction side of the pump 5.

line 48, valve 12 and line 22 tothe storage tank 2.

In case the stock is held up in the digester during the blowing operation, the valve 13 may be opened and by means of the pump 5 liquor may be forced into the bottom of the digester, thereby assisting in the removal of the cooked pulp from the digester.

My method and apparatus as above described are applicable either to acid or alkaline digestion processes. Instead of-starting the cook with hot liquor from the accumulator, it may be begun with cold acid or alkaline liquor from another source.

Material savings and an improved digestion process are effected by operation in accordance with the invention. The same lines are adapted for use in draining the digester and insupplying heat to the heating means, and the same pump is adapted for use in draining the digester and in circulating the liquor. I utilize the spent liquor contained in the digester at the end of i the cook. The selecting apparatusin the spent .liquor or steam condensate line from the heater.

automatically assures that uncontaminated liquid will be passed to the hot'well, where it may be utilized in a. variety of ways.

The heatof the heating operation may be accomplished with spent digester liquor and part with steam.

as the heating means.

Modifications of the invention being possible without departure from the spirit thereof,- I do not wish to be limited to the specific form of apparatus and method illustrated except as set forth in the appended claims.

I claim: e x

1. In apparatus of the character described, a digester, an exchange heater; a storage recep tacle and a conduit for supplying a heating medium therefrom to the exchange heater, and a conduit connecting the upper part of the die gester with the lower part thereof directly and through the exchange heater and connecting with the conduit for supplying a heating medium to the exchange heater.

2. Apparatus as described in claim 1 including a conduit for leading condensate from the exchange heater and electrically-operable means interposed in said conduit for automatically.

withdrawing therefrom condensate which is of relatively high electrical conductivity.

3. In apparatus of the character described, a digester, a heat exchanger, a storage receptacle and a conduit for supplying a heating medium therefrom to the heat exchanger, means for reversing the direction of flow of liquid in part 01- the said conduit and means for extracting liquor from the digester and passing it through said conduit to the storage receptacle.

4. In apparatus of the character described, a

. digester, an exchange heater and means for circulating liquor from the digester through the exchange heater, a storage receptacle and a conduit for extracting liquor from the digester and passing it to said storage receptacle, and means for. passing said liquor from the storage receptacle to the exchange heater.

5. Apparatus as described in claim 4 including a conduitfor supplying steam to the exchange heater and means for controlling the passage of steam therethrough and of liquor from the storage receptacle to the exchange heater.

. condensate therefrom which is of relatively high electrical conductivity.-

7. In the digestion of fibrous material," withdrawing liquor from a digester, heating said liqnor in a heat exchangerby'transfer of heat thereto from hot spent liquor and passing the digester liquor from the exchange heater through acouduit into the lower part of the digester, supplying hot spent liquor to the heat exchanger to heat the digester liquor, withdrawing, liquor from the lower part of the digester through the same conduit by which it entered the digester from the heat exchanger, andpassingsaid withdrawn liquor to a storage receptacle through the same conduit by which hot spent liquor was-supplied to the heat exchanger.

8. In the digestion of fib rous material, heating liquor from a digester and passing the heated liqheat exchanger to heat said digester liquor, then reversing the direction of flow of liquor through said conduits, withdrawing liquor from the digester and passingit through said conduits to a storage receptacle.

9. In the digestion of fibrous material, withdrawing hot spent liquor from a digester, refilling the digester with cooking liquor and initiating a cooking operation in the digester, withdrawing said cooking liquor from the digester during the cooking operation, heating the withdrawn cooking liquor by transfer of heat thereto from the hot spent liquor first withdrawn, and returning thecooking liquor thus heated to the digester.

10. In the digestion of fibrous material, withdrawing hot spent liquor from a digester, refilling the digester with cooking liquor and initiat ,ing a cooking operation in the digester, withdrawing cooking liquor from the digester during the cook, heating the withdrawn cooking liquor by a transfer of heat thereto first from the hot spent liquor first withdrawn and then from steam, and returning the heated cooking liquor to the di-' gester.

11. In a process of the character described,

heating digester liquor during the digestion process by transfer of heat from a heating medium thereto, then utilizing the electrical conductivity I of the condensed heating medium to automatically separate contaminated liquid therefrom and to permit passage of uncontaminated liquid to a storage receptacle.

12. In apparatus of the character described, a circulating system including a digester, a heat exchanger and a conduit connecting the upper part of the'digester with the lower part thereof through the heat exchanger, said conduit provided with a valved outlet from the circulating system, and having interposed therein a pump, and a by-pass connecting the lower part of the digester with the suction side of said pump through which said pump may withdraw liquor from the lower part of the digester and pass the same through said outlet without passingthe liquor through the heat exchanger.-

13. Apparatus as described in claim 12 in which the heat exchanger comprises a pair .of mutually interposed helicall'y-sloping passages.

14. Apparatus as described in claim- 12, in which the heat exchanger comprises a plurality of contiguous sections, separable from each other, which in combination form mutually interposed helically-sloping passages.

' 15:1n apparatus of the character described, a circulating system including a digester, a heat exchanger and a conduit connecting the upper "part of the digester with the lower part thereof through the heat exchanger, said conduit provided with a pump and with an outlet from the circulating system, a by-pass connecting the lower part of the digester with the suction side of-said pump and valve means on the outlet side of said pump for passing liquor from said pump either into the lower part of the digester or out of the system through the said outlet without passing through the heater.

16. In apparatus of the character described,

a digester, a heat exchanger, and means for circulating liquor from the digester through the heat exchanger, a storage receptacle and a con- 1 duit for extracting liquor from the digester and- 45 passing it to said storage receptacle and means,

which the heat exchanger comprises a pair of passages contiguous throughout their lengths, each of said passages being of unequal crosssectional diameter in difierent'directions.

18. Apparatus as described in claim 16, in which the heat exchanger comprises a plurality of juxtaposed sections, separable from each other, which in combination form curved passages contiguous throughout their lengths, said passages being of unequal cross-sectional diameter in different directions.

19. In apparatus of the character described, a digester, a heat exchanger comprising a" plurality of juxtaposed sections, separable from each other, which in combination form curved passages contiguous throughout their length, sections of the heat exchanger comprising oppositely-disposed semi-circular sheets separated at adjacent edges, means for circulating liquor from the digester through said heat exchanger and a storage receptacle connecting with said digester and with said heat exchanger.

20. In apparatus of the character described,

THOMAS L. DUNBAR. 

